1. Field of the Invention
The present invention relates to an infrared sensor and its manufacturing method, the infrared sensor having a configuration in which an infrared sensor element is accommodated in a package. More particularly, the present invention relates to an infrared sensor and its manufacturing method, the infrared sensor having a configuration in which an infrared sensor element is accommodated in a sealed space defined by a package and an optical filter which also serves as a cover.
2. Description of the Related Art
As shown in FIGS. 16A and 16B, a known infrared sensor is disclosed. See, for example, Japanese Unexamined Patent Application Publication No. 6-201454. The infrared sensor has a configuration in which an infrared sensor element 54 is accommodated in a sealed space 53 defined by a container body 51 and a stem 52, and a filter (window member) 57 is disposed at an upper surface of the container body 51. The filter (window member) 57 has a substrate 55 and infrared filter layers 56a and 56b on upper and lower primary surfaces of the substrate 55 so as to transmit infrared radiation with a predetermined wavelength.
In such an infrared sensor, as shown in FIG. 16B, a step 57a is provided at a peripheral portion of a lower surface of the filter 57. The step 57a is engaged with an opening 58 formed at the upper surface of the container body 51, and then, a metal thin film 59 which is provided on a surface of the step 57a of the filter 57 by sputtering is joined to the opening 58 of the container body 51 by using a solder 60, so that the filter 57 is attached to the opening 58 of the container body 51.
However, with the method described in Japanese Unexamined Patent Application Publication No. 6-201454, as shown in FIG. 16B, the metal thin film 59 is required to be provided on the surface of the step 57a by sputtering or the like after the step 57a is formed at the peripheral portion of the filter 57. This may cause the manufacturing procedure to be complicated, resulting in an increase in cost.
In addition, when the metal thin film 59 provided on the step 57a of the filter 57 is joined to the opening 58 of the container body 51 by using the solder 60, it is difficult to distribute the solder 60 so as to be continuously located in the peripheral portion of the opening 58 of the container body 51 for reliably joining the filter 57 to the container body 51. If the solder 60 is distributed unevenly at a gap between the step 57a and the opening 58 of the container body 51, the solder 60 may flow to the infrared filter layer 56b provided at the lower surface of the filter 57 (namely, to a center region of the infrared filter layer 56a), thereby degrading its reliability, such as that a field of view is narrowed.
As shown in FIG. 17, another infrared sensor is suggested. See, for example, Japanese Unexamined Patent Application Publication No. 10-318829. The infrared sensor has a configuration in which a step 63 is formed to be continuously arranged in a circumferential portion of an opening 62 of a ceramic package 61, and a cover 65 is fitted to the step 63. The cover 65 has an infrared sensor element 64 attached to a lower surface, and an infrared-insulating film 68 attached to an upper surface in a region not occupied by a window 67 so that only a portion (the window) 67 can transmit the infrared radiation. A filler 66 such as epoxy resin is injected to a gap between the cover 65 and the opening 62 of the ceramic package 61, and then the cover 65 is attached to the ceramic package 61.
However, with the method of Japanese Unexamined Patent Application Publication No. 10-318829, the filler 66 is not applied sufficiently to the gap between opposed surfaces of the cover 65 and ceramic package 61, resulting in unstable sealing.
If the filler 66 is sufficiently applied to the gap between the opposed surfaces of the cover 65 and ceramic package 61, the filler 66 may flow to a central region at the lower surface of the cover 65.